Dual purpose thermionic tube



July 21, 1936. H. w. PARKER DUAL PURPOSE THERMIONIC TUBE Filed Nov. 6 1934 INVENTOR Hmgg W Parker ATTORNEY Patented July 21, 1936 UNITED STATES PATENT OFFICE DUAL PURPOSE THEBBIIONIG TUBE Canada Application November 6, 1934, Serial No. 751,678

6 Claims. (Cl. 250-275) My invention relates to electron discharge devices and pertains more particularly to the type of such devices employing a plurality of thermionic discharge devices in a unitary envelope and termed dual purpose thermionic tubes.

Dual purpose thermionic tubes combining the functions of two triodes, a rectifier and a pentode, or a low mu triode and a pentode, are well known in the art but hitherto, so far as I am aware, a dual purpose thermionic tube combining the functions of a high mu triode and a power pentode has not been attempted because of the known difiiculties. It has been found very diiiicult and expensive to fabricate a thermionic tube combining the functions of a high mu triode and a power pentodein one envelope because of the necessity of completely shielding the wire lead of the high mu triode section anode from all electrostatic, electromagnetic and electron stream effects of the power pentode section of the tube, because of resistance coupling in the cathode sleeve common to both of the cathodes, the dimculty of degasifying the necessarily small and compactly disposed elements of the high mu triode section and the difficulty of achieving the necessary low capacitance between triode and pentode sections. These are difficulties which unless overcome cause non-uniformity of the manufactured product and instability of its operation.

One of the principal objects of my invention comprises, producing a simple, cheap and effective combined high mu triode and power pentode in one unitary envelope.

Another object contemplated by my invention comprises, producing a combined high mu triode and power pentode which overcomes all of the above noted difliculties.

Still another object of my invention consists in providing a combined high mu triode and power pentode tube which may be readily and cheaply fabricated and one which achieves uniformity of the product in manufacture and stability of operation in subsequent use thereof.

A further object contemplated by my invention comprises producing a combined high mu triode and power pentode tube in which the'triode section and pentode section are so completely and effectively electrically shielded from each other that each may operate effectively at its maximum emciency.

With the foregoing and other objects and desirable features in view, as will be hereinafter pointed out and discussed, my invention comprises a novel construction, combination, inter-relation and arrangements of parts as will be hereinafter more specifically described with reference to the accompanying drawing forming a part of this specification and in which like reference numeralst are employed to designate like parts through- In the accompanying drawing:

Fig. 1 is an elevation of an embodiment of my device with the enclosing-envelope partially broken away. I

Fig. 2 is a side view of the electrodes shown in 10 Fig. 1 with the enclosing envelope omitted.

Fig. 3 is a sectional view of the triode taken on the line 3-3 of Fig. 1.

Fig. 4 is a sectional view of the pentode taken on the line 4-4 of Fig. 1.

Referring now to the drawing which serves to illustrate an embodiment of my device and especially Fig. 1, there is provided a, preferably domespaced, vitreous envelope l attached to a base 2 containing the usual contact prongs as 20 shown. I, preferably, for reasons which will be discussed hereinafter, coat the exterior surface of l the envelope l and base 2 from a point near the top of the envelope l as indicated in Fig. 1 to the lower edge of the base with a metallic coating ll 25 such as described in my Patent No. 1,958,953, issued May 15, 1934. There is, provided within the envelope I which is as usual substantially exhausted of gases, a stem and press 32 which supports the electrodes constituting the triode and 30 pentode sections. The pentode section of the tube generally indicated as 30 comprises the usual anode, control grid, shield grids and cathode as shown. The arrangement and functions of the electrodes constituting a pentode is well known in 35 the art and needs no further explanation.

The cathode in my improved tube comprises the cathode sleeve I3 which is adapted to be heated by the heater 33, the terminals of which are connected to contact prongs l and 5 in the base 2. Electron emissive substances well known in the art are applied at l5 to the cathode sleeve It to serve as the cathode of the pentode 30. An additional coating of electron emissive substances is applied at M to the cathode sleeve l3 and serves as the cathode for the high mu triode section which comprises in addition the high mu control grid II and the anode l2. The anode I2 is procontrol grid of the pentode is connected to contailed explanation. The electrodes of the triode section are positioned'and maintained with respect to each other by means of discs or members II and I8 of refractory insulating material. Similarly the electrodes of the pentode 301 are positioned and maintained with respect to each other by means of refractory insulators 2| and 22. The pentode and triode sections are posi-v tioned substantially co-axially with respect to each other as shown and are shielded from each other by means of spaced metallic shields l9 and 20. These, as shown in Fig. 2, are provided with apertures through which the standards supporting the electrodes extend and are therefore insulated from such electrodes. The shields l8 and 20 are spaced apart from each other as shown in Fig. 1 and are welded to supports 23 and 2 with their surfaces each transverse to the axis of the electrodes of both the triode and pentode sections. The terminal lead for the triode section control grid is connected to the terminal ID on the top of the envelope I.

It will be noted that terminal tail 25 extending from the cathode sleeve I3 is connected to standard 23 which is likewise electrically connected to the transverse shields l9 and 20 and to the outer shield grid of the pentode. Standard 23 is connected to contact prong 9 in base 2 and serves also as a terminal for the outer shield grid of the pentode. A further cathode terminal tail 2G1 extends from the bottom of the cathode sleeve l3 and is connected tostandard 24, thus the exterior shield grid of the pentode, the transverse shields l9 and 20, and both ends of the cathode sleeve II are electrically interconnected within the envelope.

I have found that by providing a terminal tail connection for both ends of the sleeve I3, I am able to eliminate the resistance coupling in the cathode sleeve portion which is common to both of the cathodes I l and IS.

The anode l2 of the triode section is connected by means of conductor 21 as shown in Figs. 1 and 2 to contact prong 8 in the base 2. This conductor or triode anode terminal lead is preferably a tungsten wire of small diameter. It is coated with aluminum oxide which is applied to the wire in the form of finely powdered aluminum oxide mixed with aluminum nitrate and coarse grains of aluminum oxide. The mixture is baked on the wire by means of an electric furnace. This provides a ceramic coating having a very low conductivity even at extremely high temperatures. Any other ceramic having like properties may of course. be used. The conductor 21 passes through an aperture in the mica positioning shield 28. This shield serves to position the upper portion of theelectrode assembly within the envelope I and is maintained in position by strut 35 attached to the anode of the pentode 30. There is provided also a cooling vane 3| welded to the standards supporting the control grid of the pentode 20 for the purpose of increasing the radiation of heat from such grid which being relatively close to the cathode attains a high temperature during the tube operation. Vane 3| and therefore the tact prong 6 in base 2. The anode of pentode ll is connected to contact prong 3, while the inner screengrid of pentode 30 is connected to prong l.

Itwill be noted from the foregoing that through the use of an envelope provided with an exterior metallic coating as described in my patent hereinbefore mentioned, I am able to simplify the construction of the tube and its fabrication through the elimination of the large internal shields which would otherwise be necessary. The use of this metallic external shield together with the construction whereby the control grid lead of the triode section is brought out at the top of the tube and the spaced transverse shields l9 and 20 positioned between the pentode and triode sections, eliminates electrostatic coupling between the control grid of the triode and the anode of the pentode and reduces electrostatic coupling between the anode of the triode and the anode of the pentode. Through such structure I ensure the reduction to a minimum of all electrostatic and electromagnetic coupling between the two sections of the tube and by employing a wire of small diameter coated with a ceramic heat resistant insulator as the anode terminal lead of high temperature, such wire may pass through 25 the region of the tube in which there is an electron stream controlled by the pentode section and as this wire is at a high positive potential, it will not pick up any stray current from the pentode section or any current controlled by the pentode section, such structure while obviously cheap and simple, has been found to be fully as effective and eillcient as many more complicated and expensive methods now in use for similar purposes.

It will also .be obvious that I eliminate interference between the two sections of the tube by employing a cathode sleeve having two terminal tails, one at each end, one near the cathode for the triode section and one near the cathode for the pentode section. This eliminates all-resistance coupling in the hot cathode tube along its length where the triode and pentode currents are common and hence the use of both top and bottom tail terminals permits the achievement of stability and greater efliciency of performance.

It will be noted from the foregoing that I have produced a novel dual purpose thermionic tube combining the functions of a high mu triode and a power pentode in which the terminal lead of the high mu triode section is completely shielded from all electrostatic, electromagnetic and electron stream effects of the pentode section of the tube: that resistance coupling in the common cathode sleeve of the two sections is eliminated; that the difliculty of degasifying the necessarily small and compactly disposed elements of the high mu triode section is facilitated through the provision of an aperture in the triode section anode and that the necessarilylow capacitance between the triode and pentode sections is achieved through the use of spaced metallic shields transversely positioned with respect to the electrodes of the triode and pentode sections, the bringing out of the triode section lead from the top of the tube and the coating of the envelope and base with a metallic coating which cooperates with the spaced shields and the screen grids of the pentode section to permit the difierent sections of the tube to function independently and emciently.

Having thus completely described my invention what I claim as new and desire to secure by high mu triode section, a power pentode section, two metallic electrostatic shields spaced apart from each other and positioned between said triode section and said pentode section with their planes substantially transverse with respect to the electrodes constituting both said sections of said tube and a metallic coating on the exterior surface of said envelope for cooperation with said shields.

2. A dual purpose thermionic tube comprising, a substantially evacuated envelope enclosing a high mu triode section, a power pentode section, two metallic electrostatic shields spaced apart from each other and positioned between said triode section and said pentode section with their planes substantially transverse with respect to the electrodes constituting both the sections of said tube, a metallic coating on the exterior surface of said envelope for cooperation with said shields, and a wire lead attached to the anode of said triode section extending adjacent said pentode section and emerging from said envelope, said wire lead being coated for the portion of its free length within said envelope with a ceramic insulating material.

3. A dual purpose thermionic tube comprising, a substantially exhausted envelope enclosing a high mu triode section, an aperture in the anode of said triode section for observation purposes and to facilitate degasifying the elements of said section, a power pentode section and two metallic electrostatic shields spaced apart from each other and positioned between said triode section and said pentode section with their planes substantially transverse with respect to the electrodes constituting both of the sections of said tube, a metallic coating on the exterior surface of said envelope for cooperation with said shields, and a wire lead attached to the anode of said triode section extending adjacent said pentode section and emerging from said envelope, said wire lead being coated for the portion of its free length within said envelope with a ceramic insulating material.

4. A dual purpose thermionic tube comprising, a substantially exhausted envelope enclosing a high mu triode section, a power pentode section, two metallic shields spaced apart from each other and positioned between said triode section and said pentode section, a wire lead attached to the anode of said triode section extending adjacent said pentode section and emerging from said envelope and coated for the portion of its free length within said envelope with a ceramic insu- 5 lating material and a cathode sleeve common to said triode and pentode sections, terminal tabs on each extremity of said sleeve and a wire lead attached to both of said tabs and emerging from said envelope.

5. A dual purpose tube comprising, a substantially evacuated envelope, a press and stem within said envelope, a plurality of electrodes constituting a triode section, a plurality of electrodes constituting a pentode section, said sections being 15 arranged substantially co-axially above said stem,

a wire lead attached to the anode of said triode section and extending from said anode through said press in said stem, said lead wire being coated on its exposed surface with a ceramic refractory 2o insulating material, a pair of metallic shields spaced apart from each other and interposed between said triode and pentode sections with their planes transverse to the axis of said sections and a metallic coating on the major portion of 25 the exterior surface of said envelope for cooperation with said shields.

6. A dual purpose thermionic tube comprising,

a substantially exhausted envelope, a stem and press in said envelope, an indirect heated cathode 80 sleeve supported by said press, electron emissive substances disposed in disjunct regions on said sleeve, a plurality of electrodes adjacent one oi said regions of electron emissive substances and constituting a triode section, a plurality of electrodes adjacent the other of said regions of electron emlssive substances and constituting a pentode section, said cathode sleeve having terminal tabs near each of said regions of electron emissive substances, a common lead wire connected to each of said tabs and passing through said press, and a wire lead connected to one of the electrodes in said triode section extending adjacent said pentode section and through said press, said wire being coated for at least the portion thereof within said envelope with a ceramic insulating material.

HENRY W. PARKER. 

